03 yz 450 won't fire

15 replies to this topic
  • 3taz11

Posted July 30, 2008 - 10:03 PM


I rebuilt the motor and now it will not fire i have rechecked the timing I have spark and fuel any suggestions I am stumped ? I also put in a new plug still no brrrrrraaap:banghead:

  • Britincali

Posted July 30, 2008 - 10:20 PM


Pull it.

  • grayracer513

Posted July 31, 2008 - 06:32 AM


I rebuilt the motor and now it will not fire i have rechecked the timing I have spark and fuel any suggestions I am stumped ? I also put in a new plug still no brrrrrraaap:banghead:

You might want to verify that the flywheel key is properly indexed. Do this by removing the plug and finding true TDC with a Philips screwdriver, then comparing the marks on the flywheel. If they disagree significantly, you pushed the key out when you assembled it.

If you rebuilt it, the carb sat for a time, no doubt, and the fact that you have fuel at the carb doesn't mean it's getting into the engine. Check the pilot and starter jets for being lacquered over.

  • 3taz11

Posted July 31, 2008 - 10:02 PM


I cleaned the carb and checked all the wire conections , timing still nothing. Could the balance shaft be out of time ? That is the only thing I can think I might have screwed up .

  • grayracer513

Posted August 01, 2008 - 05:45 AM


You checked the timing, but did you check the timing mark, like I said?

The balancer can be in any position without affecting whether the bike will start. If it's mistimed, the engine will vibrate excessively.

  • 3taz11

Posted August 05, 2008 - 04:06 PM


yes I checked it they were good . I think I need to get a compression checker and go from there . Thank you for your input

  • shortburb

Posted August 05, 2008 - 07:55 PM


if you got into the bottom end and had the flywheel off is it back on fully so the pickup 'makes'?

  • 3taz11

Posted August 05, 2008 - 11:00 PM


ya, it is on tight

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  • desert-rat660

Posted August 08, 2008 - 08:47 PM


did u have any head work done to it? maybe the valves are hanging open a little? is the spark plug saturated with fuel? Bad gas from sitting awhile?

  • 3taz11

Posted August 10, 2008 - 10:18 PM


we did not do any head work ,that is what we are going to do next thank you

  • TD-3

Posted August 11, 2008 - 03:13 AM


You had the head off and cams out, did you check the valve shims to make sure they're seated correctly? I had this happen to me.

When the head is off and the cams are out, the buckets can slide up taking the shims with them and not seat correctly when puhed back down. You can verify by checked valve clearance.

  • shortburb

Posted August 11, 2008 - 10:23 AM


+1 on shims holding valves open...

i didnt check them before i put mine together and when i kicked it through it felt easy like it didnt have much compression(more so than even with auto decomp)...pulled the VC and checked valves and one of them was sitting funny, leaving a valve open

  • desert-rat660

Posted August 11, 2008 - 05:05 PM


i had the same thing happen but i caught it before installing the cam

  • 3taz11

Posted August 11, 2008 - 08:27 PM


we have braaap:applause: :) it was those LITTLE :D shims we checked the clearance and there was none on the outside vavle . Thank you guys for all of your help!! Lesson learned:prof:

  • desert-rat660

Posted August 11, 2008 - 08:34 PM


no problem

  • TD-3

Posted August 12, 2008 - 02:43 AM



Good deal! :D

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